FR2911517A1 - Carbondioxide gas separating method for e.g. purifying carbondioxide gas, involves dispersing nitrogen and carbondioxide gas mixture in liquid phase at specific temperature and at pressure equal to/higher than atmospheric pressure - Google Patents

Abstract

The method involves suspending a porous product that captures carbondioxide gas, in a liquid phase, where the porous product is chosen from activated carbon, zeolite and quintinite-3T. A nitrogen and carbondioxide gas mixture is dispersed in the liquid phase at a temperature ranging between zero and 100 degree celsius and at a pressure that is equal to/higher than an atmospheric pressure. The captured carbondioxide gas is collected.

Description

The present invention relates to a process for separating 002 gas

  contained in a gas mixture. The separation of 002 gas contained in a gas mixture is of interest in many fields of application. In particular, we can mention the fight against global warming, an area for which greenhouse gas trapping is essential. We can also mention the purification of 002 with a view to its commercialization as well as the depollution of industrial gaseous discharges. Various methods are known, whether these are of a physical or chemical type, making it possible to ensure the separation of 002 from a gas mixture, in particular to trap it and / or purify it. A widespread technique is based on the use of amines and more specifically on the use of the monoethanolamine solvent (see US-4,477,419). This method, interesting as it is, has drawbacks in terms of transport because of the nature of the solvent used. On the other hand, many impurities such as NOX and SO 2 degrade the amines thereby decreasing the efficiency of the process. It has also been proposed to use mineral traps whose ability to promote the physisorption or even the capillary condensation of the gas in appropriate gas phase porosity (see Yong et al, Separation and Purification Technology 26 (2002)). 195-205). These traps consist in particular of aluminas, zeolites, active carbons or hydrotalcite-type minerals. A problem of this technique is however to require the implementation of high pressures and high temperatures that are necessary for the realization of capillary condensation and desorption phenomena.

  A recent technique, antisublimation, in which the operation is carried out at atmospheric pressure by the direct passage of the vapor phase to the solid phase of 002 on the outer surface of refrigeration exchangers, has also been used. temperatures between -80 ° C. and -110 ° C. (see FR-2,820,052 and FR-2,851,936). This process also requires the implementation of significant energy. It has also been proposed to cross the flow of gaseous mixture from which it is desired to separate some of the constituents through a membrane made of a material having a permeability which is a function of the component which it is desired to isolate during this passage (cf. Vallières and Favre, Journal of Membrane Science 244 issues 1-2 (2004) 17-23). It has been used to constitute such a membrane to many mineral and polymeric materials. This technique has the disadvantage of only allowing the effective treatment of low gas flows.

  Finally, the Applicant has recently proposed in the French patent application No. 05 11 687 to separate and / or purify gases, some of which are capable of forming anionic species in the aqueous phase with HDL type solids or mixed oxides from the treatment. thermal HDL. The present invention aims to overcome the disadvantages of known techniques, by providing a method for separating gaseous CO2, contained in a gaseous mixture, effective and low cost.

  To this end, the subject of the present invention is a method for separating gaseous CO2 contained in a gas mixture comprising: a step of suspending in a liquid phase a porous solid capable of capturing gaseous CO2, and a diffusion step of the gas mixture in the liquid phase, said step being carried out at a temperature between 0 C and 100 C and at a pressure equal to or greater than atmospheric pressure. The invention is based on the surprising finding, verified experimentally by the inventors, that the amount of CO2 trapped by a porous solid suspended in a liquid phase is much greater than that retained by the same solid in the gas phase. The method according to the invention is also particularly advantageous in that it can be conducted at ambient temperature and pressure conditions, or close to ambient conditions, and therefore at low cost. Preferably, the diffusion step is carried out at a temperature of between 0 ° C. and 30 ° C. In particular, the porous solid is chosen from an activated carbon, a zeolite or a 3T quintinite.

  Advantageously, the process comprises an additional step of recovering the gaseous CO2 captured. The combination of the trapping and recovery stages makes it possible to carry out a purification of the CO2. This recovery step preferably comprises a step of lowering the partial pressure of the gas to be trapped introduced into the liquid phase and / or a step of raising the temperature of the liquid phase. Finally, the process may comprise iteratively the cycle formed of a step of diffusion of the gas mixture and a recovery step.

  Various embodiments of the present invention will be described hereinafter by way of nonlimiting example, with reference to the appended drawing, in which: FIG. 1 is a diagram schematically showing the process according to the invention; FIG. 2 is a curve showing, as a function of time, the concentration of CO2 in the exit gas stream during capture and release phases by activated carbon, FIG. 3 is a curve representing as a function of time , the concentration of CO2 in the exit gas stream during capture and release phases by a zeolite-rich material, and - Figure 4 is a curve showing, as a function of time, the concentration of CO2 in the gas stream in the course of capture and release phases repeated iteratively by a 3T quintinite. According to the invention and as schematized in FIG. 1, there is a mixture of several gases, one of which is CO2 which it is desired to extract from the mixture in order to trap it and, if appropriate, to subsequently return it under purified form. For this, the method comprises a first step 2 in which a porous solid suitable for trapping the CO2 is suspended in a liquid medium. It comprises a second step 4 in which the gaseous mixture is diffused in the liquid medium. In practice, the liquid medium is disposed in a reactor comprising an inlet for admitting the gas mixture and an outlet for extracting the uncaptured gas mixture after treatment or carbon dioxide after liberation.

  Steps 2 and 4 trap the CO2 contained in the gas mixture. In an advantageous embodiment, the method may comprise a third step 6 for recovering CO2. The release of trapped CO2 in the trap material can be achieved by reducing the partial pressure of the CO 2 at the inlet of the reactor, and / or by increasing the temperature of the liquid medium. In the case where it is desired to extract purified CO2, it is preferable to completely close the gas inlet of the reactor, the output gas of the reactor then comprising only carbon dioxide. In the context of an industrial process, steps 4 and 6 are repeated iteratively, as indicated by arrow 8, by opening and closing the reactor gas inlet to produce at the outlet of the reactor, when the inlet gas is closed, pure CO2. Three examples of methods according to the invention will be described below. EXAMPLE 1 Activated carbon A capture and then release test of CO2 from a stream of a gaseous mixture N2 / CO2 was carried out by a trap formed of activated carbon suspended in an aqueous medium. The activated carbon used has a specific surface area of 1500 m 2 / g.

  The initially introduced gas mixture has an initial CO2 content of 19% by volume, which has then been raised to 76% by volume. The treatment was carried out at a temperature of 15 C and at atmospheric pressure. The CO2 content in the reactor outlet mixture is shown in FIG.

  During a period between t0 (initial time) and t2, the content of 002 in the input gas mixture is 19% by volume. During this period, the content of 002 in the outlet gas increases from 0% at time t0 up to 19% up to a time t1, which indicates a capture of 002 by the trap, then stabilizes at 19% between t1 and t2, indicating that a balance is reached. At time t2, the composition of the input gas mixture is modified by increasing the content of 002 to 76% by volume up to a time t4. This modification of the 002 content is carried out as part of a laboratory test. In an industrial process, it is generally not possible to proceed with such a modification of the gas mixture. It can be seen that, as during the period t0-t2, the output content of 002 increases between t2 and an instant t3, marking a capture of CO2r and then stabilizes at 76% by volume from t3 when a new equilibrium is reached. .

  The volumes of 002 captured for a content of 002 of 19 and 76% respectively represent 0.5 mole of CO2 / kg of activated carbon and 0.77 mole of CO2 / kg of activated carbon. It is thus noted that the capture is even better than the partial pressure of 002 in the gas mixture is important. At time t4, we stop supplying 002 into the reactor (nitrogen supply alone). At the outlet of the reactor, the release of the captured 002 is observed until a time t5. The amount of gas released is of the order of 3.3 mol of CO2 / kg of activated carbon. This quantity is greater than that captured during the two capture phases. This is most likely due to the release of oxygenated groups present on the activated carbon surface prior to testing. When the temperature is raised to 60 ° C., an additional release of 0.18 mol of residual CO 2 / kg of activated carbon is observed (see period t5-t6). EXAMPLE 2 Zeolite A test similar to the previous one was carried out by replacing the activated carbon with a material rich in zeolite whose specific surface area is close to 70 m 2 / g. As can be seen in FIG. 3, the same type of curve is observed as in the previous test for the output content of 002: period t0-t2: N2 / CO2 mixture at 19% of 002, reactor at 15 VS; capture of 002 until an equilibrium is reached; t2-t4 period: N2 / CO2 mixture at 76% of 002, reactor at 15 ° C .; additional capture of 002 until a new equilibrium is reached, - period t4-t5: no contribution of CO2r reactor at 15 C; liberation of CO2r 20 - period t5-T6: no contribution of 002r reactor at 60 C; In this example, the volumes of 002 captured for 002 contents of 19 and 76% are respectively 0.54 moles of CO2 / kg of zeolite and 2.08 moles of CO2 / kg of zeolite, a total amount of 2.62 moles of CO2 / kg of zeolite. At time t5, a release of 2.65 moles of CO2 / kg of zeolite is observed, which corresponds substantially to the portion collected. An additional release of 0.39 mole CO2 / kg of zeolite is observed when the reactor is heated to a temperature of 60 ° C.

  EXAMPLE 3: Quintinite 3T The test was carried out with a porous solid having a specific surface area of 80 m 2 / g placed in aqueous suspension in a reactor at 30 ° C. and at atmospheric pressure. The input gas is a N2 / 002 mixture, the CO2 content being 9% by volume. During the supply of the gas mixture (period t0-t1 in Figure 4), the CO2 is captured until a balance is reached. Under the conditions of the test, 0.49 mole CO2 / kg of 3T quintinite is captured. Then, in the absence of CO2 input (period tl-t2 in FIG. 4), the CO2 captured is released. A release of 0.49 mole CO2 / kg quintinite 3T is observed, which corresponds to the captured part.

  In this test, the capture step was repeated by feeding the reactor back with the gas mixture. There is a catch of 0.67 mole CO2 / kg of 3T quintinite. Thus, in the context of an industrial use of the process, it is found that by a succession of capture / release cycles, each cycle comprising a step of supplying a gas mixture followed by a step without the addition of CO2 or without the addition of a gas mixture, it is possible to extract CO2 from a gas mixture while purifying it.

  In the tests described above, carried out in the laboratory, the nitrogen is continuously supplied to the reactor, this to better highlight in Figures 2 to 4 the decreasing CO2 output of the reactor, which reflects its release.

  It is obvious that, in the context of an industrial use of the process, it is not possible to stop the supply of CO 2 alone in the mixture introduced into the reactor. In such a context, the gas supply to the reactor is simply interrupted to cause the release of CO2. It will also be possible to facilitate this release apply a slight depression downstream of the reactor. The method according to the invention is therefore particularly interesting from an industrial point of view. Indeed, it allows the trapping of CO2 in a reversible manner without using energy-intensive processes (high temperature rise, evaporation of a liquid phase, solid / liquid separation, etc.) and without any manipulation of the suspension constituting the trap that remains in place in the capture / release reactor for the duration of the cycles. Moreover, the process is carried out under conditions of ambient pressure and temperature or near ambient conditions, a slightly higher temperature favoring the release of CO2.

Claims (7)

  1. A process for separating gaseous 002 contained in a gas mixture comprising: a step of suspending in a liquid phase a porous product capable of capturing the gaseous gas; a step of diffusion of the gas mixture. in the liquid phase, said step being carried out at a temperature between 0 C and 100 C and at a pressure equal to or greater than atmospheric pressure.   2. The process according to claim 1, wherein the diffusion step is carried out at a temperature between 0 ° C. and 30 ° C.   3. A process according to one of claims 1 or 2, wherein the capture product is selected from an activated carbon, a zeolite or a 3T quintinite.   4. A process according to one of claims 1 to 3, comprising an additional step of recovering the gaseous gas captured.   5. A process according to claim 4, wherein said recovering step comprises a step of lowering the partial pressure of the gas to be trapped introduced into the liquid phase and / or the depression of the capture reactor.   6. Method according to one of claims 4 or 5, wherein said recovery step comprises a step of raising the temperature of the liquid phase.   7. A process according to claim 4, wherein the cycle consisting of a diffusion step and a recovery step is repeated iteratively.